In recent years, many semiconductor storage devices (3-dimensional semiconductor storage devices) formed by arranging memory transistors (memory cells) in a 3-dimensional structure have been proposed to increase the degree of memory integration. For example, the conventional 3-dimensional semiconductor storage device has a columnar semiconductor layer extending in a direction perpendicular to a substrate and an electroconductive layer that surrounds the columnar semiconductor layer via a charge-accumulating layer. The columnar semiconductor layer functions as the body of the memory transistor. The electroconductive layer functions as a word line connected to the gate of the memory transistor and the memory transistor.
For the columnar semiconductor to better function as the body of the memory transistor, it is necessary to increase the mobility of the carrier in the columnar semiconductor layer. However, voids may be formed inside the columnar semiconductor layer when the columnar semiconductor layer is formed. When the voids move and make contact with the gate insulating film, the memory strings cannot function with the desired characteristics.